1. Field of the Invention
The present invention relates to a method and an apparatus for automatically analyzing a trace substance, and more Particularly, to a method and an apparatus for automatically analyzing a desired gaseous substance or substances existing in an atmosphere, which are preferably applied to monitoring gaseous contaminants existing in a clean room used in the field of semiconductor device fabrication.
2. Description of the Prior Art
A trace of gaseous contaminant remaining in a clean room atmosphere tends to increasingly cause failures or defects in next-generation semiconductor devices during their fabrication process steps. To stabilize the prosecution of the mass-production processes of the next-generation semiconductor devices, usually, suitable dust/chemical filters are used for removing dusts and chemicals existing in the air in the clean room. However, there is a possibility that contamination accidents occur due to supplied source materials for fabrication processes and that the dust/chemical filters may be damaged or broken due to contaminants. Thus, it is required to automatically and continuously measure and monitor contaminants existing in the air in a clean room.
In a prior-art multi-point measuring method for measuring trace contaminants at different positions in a clean room, desired gaseous contaminants are sampled from the air and then, concentrated to specific concentrations corresponding to the lower limit of an analytical apparatus or instrument by using the impinger method while taking a lot of time, thereby analyzing and quantitative analyzing the concentrated contaminants. However, there is a problem that the measuring interval of time is too long and the total amount of the contaminants at the measuring positions is unable to be determined, and that an outbreak of a high-concentration contaminant is unable to be well-treated.
On the other hand, there is a known prior-art multi-point analyzing method for automatically analyzing ammonia existing in a clean room atmosphere using a diffusion scrubber. FIGS. 1 and 2 show prior-art multi-point ammonia analytical apparatuses that perform this analyzing method, which are disclosed in the Japanese Non-Examined Patent Publication No. 8-54380 published in June 1994 and its corresponding U.S. Pat. No. 5,714,676 issued on Feb. 3, 1998.
In FIG. 1, the prior-art multi-point ammonia analytical apparatus is comprised of a sampler 1100, a concentrator 1200, and an analyzer 1300. The sampler 1100 has a switch valve 601 with ten inlets connected respectively with ten sampling points P1 to P10 located in the clean room, and a diffusion scrubber 602 connected to an outlet of the valve 601. The concentrator 1200 includes a concentration column 604 of an ion chromatograph 603. The analyzer 1300 includes a separation column 605, a suppressor 606, and an electrical conductivity meter 607 of the ion chromatograph 603. A controller 608 controls the whole operation of the sampler 1100, the concentrator 1200, and the analyzer 1300.
With the prior-art analytical apparatus of FIG. 1, the total measuring time Ttotal for all the sampling points P1 to P10 is expressed as the following equation (1), where n is the number of the sampling points, and Tpt, Tr, Ts, and Tsa are the times for the pre-treatment operation, the rinsing operation, the sampling operation, and the separation/analyzing operation, respectively.
Ttotal=nxc3x97(Tpt+Tr+Ts+Tsa)xe2x80x83xe2x80x83(1)
The schedule of the individual operations for the sampling points P1 to P10 is shown in FIG. 2. Specifically, at first, the pre-treatment and sampling operations are successively carried out for the sampling point P1 and then, the rinsing and separation/analysis operations for the same point P1 are successively carried out. Next, the same time schedule is successively repeated for each of the points P2 to P10.
In the prior-art analytical apparatus of FIG. 1, the switch valve 601 of the sampler 1100 assigns alternately one of the sampling points P1 to P10 to the diffusion scrubber 602. Thus, there is a problem that the total measuring time Ttotal for all the sampling points P1 to P10 is very long.
For example, if the time Tpt for the pre-treatment operation is 25 minutes, the time Tr for the rinsing operation is 0.5 minute, the time Ts for the sampling operation is 7.5 minutes, and the time Tsa for the separating/analyzing operation is 8 minutes, the total time Ttotal is 410 minutes.
The prior-art multi-point ammonia analytical apparatus shown in FIG. 3 is comprised of a sampler 2100, a concentrator 2200, and an analyzer 2300.
The sampler 2100 has a switch valve 701a having five inlets connected respectively with five sampling points P1 to P5, a diffusion scrubber 702a connected to an outlet of the valve 701a, a switch valve 701b having five inlets connected respectively with five sampling points P6 to P10, and a diffusion scrubber 702b connected to an outlet of the valve 701b. 
The concentrator 2200 is comprised of a concentration column 704 of an ion chromatograph 703. The analyzer 2300 is comprised of a separation column 705, a suppressor 706, and an electrical conductivity meter 707 of the ion chromatograph 703.
A controller 708 controls the whole operation of the sampler 2100, the concentrator 2200, and the analyzer 2300.
With the prior-art analytical apparatus of FIG. 3, the controller 708 controls so that one of the valves 701a and 701b is used for the pre-treatment operation while the other of the valves 701a and 701b is used for the rinsing, sampling, and separation/analysis operations. The schedule of the individual operations for the sampling points P1 to P10 is shown in FIG. 4.
Thus, the total measuring time Ttotal for all the sampling points P1 to P10 is expressed as the following equation (2) under the condition that the following inequality (3) is established.
Ttotal=nxc3x97(Tr+Ts+Tsa)xe2x80x83xe2x80x83(2)
Tptxe2x89xa7Tr+Ts+Tsaxe2x80x83xe2x80x83(3)
The inequality (3) means that the time Tpt for the pre-treatment operation is equal to or greater than the sum of the times for the rinsing, sampling, and separation/analysis operations, i.e., (Tr+Ts+Tsa).
In the prior-art analytical apparatus of FIG. 3, for example, if the time Tpt for the pre-treatment operation is 25 minutes, the time Tr for the rinsing operation is 0.5 minute, the time Ts for the sampling operation is 7.5 minutes, and the time Tsa for the separating/analyzing operation is 8 minutes, the total time Ttotal is 185 minutes. Thus, there is a same problem that the total time measuring time Ttotal for all the sampling points P1 to P10 is still long.
Moreover, gaseous ammonia tends to remain in the sampler 1100 or 2100 and the concentrator 1200 or 2200 after a sampled air with high-concentration ammonia is measured. The remaining ammonia or residue in a prior measuring step affects badly a subsequent measuring step. This is called the xe2x80x9cmemory effectxe2x80x9d of the residue.
In particular, when an organic substance such as monoethanolamine is analyzed and measured in the above-described prior-art apparatuses of FIGS. 1 and 3, the organic substance is extremely easy to remain in the inside of the apparatuses. Thus, correct measurement is unable or very difficult to be carried out.
Accordingly, a general object of the present invention to provide a method and an apparatus for automatically analyzing a trace substance capable of automatic analysis of a trace substance in a short time with high accuracy.
A specific object of the present invention to provide a method and an apparatus for automatically analyzing a trace substance that decreases the time for each cycle of measurement or analysis.
Another specific object of the present invention to provide a method and an apparatus for automatically analyzing a trace substance that simplifies the structure of the sampler.
Still another specific object of the present invention to provide a method and an apparatus for automatically analyzing a trace substance that suppress the memory effect due to a residue of the substance.
A further specific object of the present invention to provide a method and an apparatus for automatically analyzing a trace substance capable of monitoring the occurrence or outbreak of an abnormal concentration of the substance.
A still further specific object of the present invention to provide a method and an apparatus for automatically analyzing a trace substance capable of monitoring the cumulative sum of the substance in a specific period of time.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to a first aspect of the present invention, an apparatus for automatically analyzing a trace substance is provided, which is comprised of (a) samplers for making samples each containing a desired substance at different sampling points, (b) concentrators for concentrating the substance contained in the samples to thereby produce concentrated samples, (c) a quantitative analyzer for analyzing quantitatively the substance contained in the concentrated samples, and (d) a controller for controlling the samplers, the concentrators and the analyzer to cause automatically operations of the samplers, the concentrators, and the analyzer repeatedly at specific intervals of time.
Each of the concentrators receives alternatively the samples from at least two ones of the samplers.
The analyzer receives alternatively the concentrated samples from the concentrators.
With the apparatus for automatically analyzing a trace substance according to the first aspect of the present invention, each of the concentrators receives alternatively the samples from at least two ones of the samplers, and the analyzer receives alternatively the concentrated samples from the concentrators. Therefore, the analyzer can receive alternatively the concentrated samples from the concentrators without waiting or idle time under the control of the controller. Accordingly, the time for each cycle of measurement or analysis can be decreased.
Also, since each of the samplers makes the corresponding sample containing the desired substance at the different sampling points, each of the samplers can make the samples by using common sampling tubes connected to the respective sampling points. Thus, the structure of the samplers is simplified.
Moreover, since the analyzer receives alternatively the concentrated samples from the concentrators, an unused one or ones of the concentrators and its relating samplers can be cleaned or rinsed while the analyzing operation of the used one of the concentrators is performed. Thus, the memory effect due to a residue of the substance can be suppressed.
As a result, the apparatus according to the first aspect of the present invention has an advantage that automatic analysis of a trace substance can be realized in a short time with high accuracy.
In a preferred embodiment of the apparatus according to the first aspect, the desired substance is gaseous and each of the concentrators has a diffusion scrubber and a concentration column.
In another preferred embodiment of the apparatus according to the first aspect, the desired substance is gaseous and each of the concentrators has four diffusion scrubbers and two concentration columns.
In still another preferred embodiment of the apparatus according to the first aspect, the analyzer has a function of ion chromatograph.
In a further preferred embodiment of the apparatus according to the first aspect, the controller has a function of monitoring an outbreak of a high-concentration state of the substance. In this embodiment, there is an additional advantage that the occurrence or outbreak of an abnormal concentration of the substance can be monitored.
In a still further preferred embodiment of the apparatus according to the first aspect, the controller has a function of calculating a cumulative sum of the substance in a specific period of time. In this embodiment, there is an additional advantage that the cumulative sum of the substance in a specific period of time can be monitored.
In a more further preferred embodiment of the apparatus according to the first aspect, a cleaner for cleaning the samplers by supplying a purging gas into the samplers is additionally provided.
It is preferred that the cleaner is comprised of a container for containing the purging gas, and a valve for selecting one of flow paths for the samples and for the purge gas.
Each of the diffusion scrubbers may have the cleaner.
According to a second aspect of the present invention, another apparatus for automatically analyzing a trace substance is provided, which is comprised of (a) a sampler for making a sample containing a desired substance at a sampling point, the sampler including a diffusion scrubber, (b) a concentrator for concentrating the substance contained in the sample to thereby produce a concentrated sample, the concentrator including a concentration column, (c) a quantitative analyzer for analyzing quantitatively the substance contained in the concentrated sample, (d) a cleaner for cleaning the sampler by using a purging gas, and (e) a controller for controlling the sampler, the concentrator, the analyzer, and the cleaner to cause automatically operations of the sampler, the concentrator, the analyzer, and the cleaner repeatedly at specific intervals of time.
With the apparatus for automatically analyzing a trace substance according to the second aspect of the present invention, because of the cleaner being provided, the memory effect due to a residue of the substance can be suppressed.
In a preferred embodiment of the apparatus according to the second aspect, the cleaner is comprised of a tank for storing a purging gas, and a valve for connecting the tank with the diffusion scrubber of the sampler.
In another preferred embodiment of the apparatus according to the second aspect, an additional sampler for making an additional sample containing the desired substance at a sampling point, the additional sampler including a diffusion scrubber. The two diffusion scrubbers of the samplers are alternately connected to the concentrator. The cleaners are designed for cleaning the two samplers.
According to a third aspect of the present invention, a method for automatically analyzing a trace substance is provided, which is performed in the apparatus according to the first aspect.
This method includes a xe2x80x9cpre-treatment operationxe2x80x9d for supplying an absorbing liquid to at least one of the samplers to suppress the effect of a residue of the substance generated in a prior measurement step, a xe2x80x9crinsing operationxe2x80x9d for rinsing an eluting liquid remaining in one of the concentrators, a xe2x80x9csampling operationxe2x80x9d for making the samples by the samplers and for making the concentrated samples by the concentrators, and a xe2x80x9cseparation/analysis operationxe2x80x9d for separating the substance from the samples and for quantitatively analyzing the separated substance.
Moreover, a time of the xe2x80x9cseparation/analysis operationxe2x80x9d is equal to the sum of a time of the xe2x80x9crinsing operationxe2x80x9d and a time of the xe2x80x9csampling operationxe2x80x9d.
With the method according to the third aspect of the present invention, the total analyzing time is minimized.
According to a fourth aspect of the present invention, another method for automatically analyzing a trace substance is provided, which is performed in the apparatus according to the first aspect equipped with the cleaner.
This method includes a xe2x80x9ccleaning operationxe2x80x9d for cleaning the samplers using the purging gas, a xe2x80x9cpre-treatment operationxe2x80x9d for supplying an absorbing liquid to at least one of the samplers to suppress the effect of a residue of the substance generated in a prior measurement step, a xe2x80x9crinsing operationxe2x80x9d for rinsing an eluting liquid remaining in one of the concentrators, a xe2x80x9csampling operationxe2x80x9d for making the samples by the samplers and for making the concentrated samples by the concentrators, and a xe2x80x9cseparation/analysis operationxe2x80x9d for separating the substance from the samples and for quantitatively analyzing the separated substance.
Moreover, a time of the xe2x80x9cseparation/analysis operationxe2x80x9d is equal to the sum of a time of the xe2x80x9ccleaning operationxe2x80x9d and a time of the xe2x80x9cpre-treatment operationxe2x80x9d.
With the method according to the fourth aspect of the present invention, the total analyzing time is minimized.
According to a fifth aspect of the present invention, still another method for automatically analyzing a trace substance is provided, which is performed in the apparatus according to the second aspect.
This method includes a xe2x80x9ccleaning operationxe2x80x9d for cleaning the sampler using the purging gas, a xe2x80x9cpre-treatment operationxe2x80x9d for supplying an absorbing liquid to the sampler to suppress the effect of a residue of the substance generated in a prior measurement step, a xe2x80x9crinsing operationxe2x80x9d for rinsing an eluting liquid remaining in the concentrator, a xe2x80x9csampling operationxe2x80x9d for making the sample by the sampler and for making the concentrated sample by the concentrator, and a xe2x80x9cseparation/analysis operationxe2x80x9d for separating the substance from the sample and for quantitatively analyzing the separated substance.
Moreover, a time of the xe2x80x9cseparation/analysis operationxe2x80x9d is equal to the sum of a time of the xe2x80x9ccleaning operationxe2x80x9d and a time of the xe2x80x9cpre-treatment operationxe2x80x9d.
With the method according to the fifth aspect of the present invention, the total analyzing time is minimized.